Subject - In this case, this will either be 'there' before a noun phrase, or 'the number of earthquakes each year' followed by a verb phrase. 

 

Verbs - When describing verbs, I shall talk about the 1st, 2nd and, 3rd forms of a verb.

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• The 1st is the base / bare infinitive. e.g. be (is, am, are), see, want

• The 2nd is the past from e.g. was/were, saw, wanted

• The 3rd is the past participle e.g. been, seen, wanted

 

​We can use any of these verb forms with an adjective to make a verb phrase. 

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     Each letter below corresponds to a section of the line chart below. I will explain why each tense is used, give a general structure to form the tense, and then give examples for both noun and verb phrases describing the graph above. 

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A - When describing a single point in time, we must use past simple tense. This is mostly the tense we have used so far in these 'change over time' lessons. 

 

Past simple = subject + verb (2nd form)  

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In 2015, there were 20 earthquakes. 

Between 2015 and 2017, there was a steady growth in the number of earthquakes.

The number of earthquakes steadily grew between 2015 and 2017.

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B - If we are talking about a change that happens entirely in the past, we can use the past perfect tense. We use this tense if we want to focus on the result of a change in the past on a different time in the past. Look at the end of the change, and describe what happened up to that point in time. 

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Past perfect = subject + had + verb (3rd form)  

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By 2019, the number of earthquakes had increased by 60 per year. 

By 2019, there had been an increase of 60 earthquakes per year.

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     In these examples, the change happened before 2019 (2016, 2017 etc,) but we are focused on the result of that change in 2019. 

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C - If you have the present in your line chart (in our case, 2022), we can use the present perfect tense. Like past perfect, we use this if we want to focus on the result of a change, but this time it's the result of the change now. We can use the preposition 'since' with this tense, which means from a time in the past until today. 

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Present perfect = subject + have / has + verb (3rd form)  

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Since 2019, the number of earthquakes per year has dropped by 20. 

Since 2019, there has been a drop of 20 earthquakes per year.

 

D - You can also sometimes use the present simple tense to describe a single point in time in the present. In this case, we cannot do that, as the earthquakes are not likely to have happened right at the time of speaking. ​

 

Present simple = subject + verb (1st form)  

 

E - English doesn't really have a future tense. We instead use lots of different verb choices to show that we are discussing the future. Most commonly we use the auxiliary verb 'will' or 'going to' with a verb to show the fact it's in the future. However, we can also use verbs such as  'predict' and 'estimate' with passive voice, to show that someone has made these figures.

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Future simple = subject + will + verb (1st form)  OR 

subject + is / am / are + going / predicted / estimated + to + verb (1st form)  

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Between today and 2025, the number of earthquakes will fall to only 10 per year.

Over the next three years, there is going to be a fall in the number of earthquakes each year to only 10. 

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Between today and 2025, there is predicted to be a fall in the number of earthquakes with only 10 in each year. 

Over the next three years, the number of earthquakes is expected to drop to 10 each year.

 

F - We can also use the perfect aspect in the future, to show what is expected to have changed by a point in the future. 

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Future perfect = subject + will + have + verb (3rd form)  OR 

subject + is / am / are + going / predicted / estimated + to have + verb (3rd form)

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By 2025, there is predicted to have been a fall in the number of earthquakes with only 10 in each year. 

By 2025, the number of earthquakes is expected to have fallen to 10 each year.

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The perfect aspect is a great way to show that you can use a wider range of grammar in your answers.